a) Field of the Invention
The present invention relates to contact strips for photographs used on electric railcars, and more particularly to a contact strip for a pantograph (will be referred to simply as "contact strip" hereinafter) used on the electric railcar which collects the current from the trolley wire while sliding on the trolley wire without any lubricating oil, and which is lightweight, highly resistant against abrasion and thus suitably usable on a high-speed electric railcar such as the Japanese Shinkansen-line railcars running at a speed higher than 200 km/hour.
b) Description of the Prior Art
Generally, a plurality of the contact strips 20 are connected in series with each other and also in the proximity of each other on the collector heads or collecting shoes 12 fixed in two rows atop the pantograph 10 of an electric railcar. In the case of the Japanese Shinkansen-line electric railcars, for example, six contact strips are fixed on one pantograph, that is, three on each collector head, while in the case of the Japanese existing-railway electric railcars, eight contact strips are fixed on one pantograph, that is, four on each collector head. The electric locomotives have provided twelve contact strips on one pantograph, that is, six on each collector head. As shown in FIGS. 2 (A) and (B), the structure of the conventional contact strips 20 used on such electric railcars is wholly made of a sintered alloy of the same materials. It is required that the contact strips should have excellent mechanical characteristics such as tensile strength, value of impact energy, hardness, etc. and a resistivity, corresponding to the speed of the electric railcar on which they are to be used. The current Standard for the Japanese Shinkansen-line electric railcars requires that the iron-based abrasion-resistant sintered alloys be more than about 7 in specific gravity and copper-based abrasion-resistant sintered alloys be more than 8 in specific gravity. Materials having lower specific gravities those set forth above cannot meet the mechanical and electrical requirements needed for use on the Shinkansen-line electric railcars. Such conventional abrasion-resistant sintered alloys are disclosed in the Japanese Examined Patent Publications (Kokoku) No. Sho 55-44143, 54-42332, 52-24487 and 50-36809.
The current Japanese Shinkansen-line electric railcars Standard for the contact strips requires that the thickness T be 10 mm, width W be 25 mm and length L be 270 mm. Namely, the iron-based abrasion-resistant sintered alloy should be about 480 g in weight per contact strip, while the copper-based abrasion-resistance sintered alloy should be about 560 g in weight per contact strip. As previously mentioned, six contact strips are used on one pantograph of the Shinkansen-line electric rail car such that the total weight of the contact strips if they were made of the iron-based abrasion-resistant sintered alloy would be about 2,880 g while the total weight of the contact strips if made of the copper-based abrasion-resistant sintered alloy be 3,360 g.
Since the current contact strips for the electric rail cars are considerably heavy, the electric rail cars are driven by a current while the pantograph is being forced against the trolley wire from below by a lifting spring force of 5.5 kg. However, as the electric railcar speed increases, the follow-up, or connection, of the contact strips with the trolley wires becomes degraded and arcing takes place between them, so that the arcing-caused abrasion of the trolley wires and contact strips increases. That is to say, the abrasion of the contact strips and trolley wires, caused while the electric railcar is running, is a sum of the abrasion due to the mechanical sliding of the contact strips fixed against the pantograph on the trolley wires and the arcing-caused abrasion. Namely, the arcing-caused abrasion will increase because the follow-up of the contact strips with the trolley wire becomes worse as the railcar runs at a higher speed.